Petroleum systems modeling and simulation are commonly used in the oil & gas industry to model the structure and/or properties of subsurface formations, e.g., of the type containing recoverable hydrocarbons. Petroleum systems modeling and simulation may be used during various phases of exploration and production, including, for example, to attempt to predict the location, quantity and/or value of recoverable hydrocarbons, to plan the development of wells for cost-effectively extracting hydrocarbons from the subsurface formation, and to guide future and/or ongoing production and development decisions.
Petroleum systems modeling is a particular type of subsurface modeling that attempts to model, amongst others, the petroleum generation potential of a sedimentary basin, generally by modeling geologic, thermal and fluid-flow processes in and around the sedimentary basin over a time period on the order of millions of years. A sedimentary basin is understood to be a region of the Earth of long-term subsidence (i.e., downward shifting of the Earth) creating the conditions for infilling by sediments, and understanding the evolution of such basins has been found to provide useful insight for locating potential hydrocarbon reserves. Sedimentary basins may form in response to various geological processes. For example, one type of sedimentary basin, referred to a rift basin, generally forms as a result of continental rifting, and is generally characterized as an elongate crustal depression bounded on one or both sides by basement-involved normal faults.
One particular uncertainty in petroleum system modeling is the amount of heat that has entered sedimentary basins from below, also known as basal heat flow. In rift basins, for example, the lithospheric layer thicknesses of the outer earth can be a notable factor when defining basal heat flow. Conventional approaches used to generate thickness variations apply an isostatic principle to a stretching model in order to invert the observed subsidence into a thickness variation of the lithospheric layers. However, it has been found that the behavior described in these models may not describe the stretching within the upper mantle in a geologically reasonable way.
With respect to rift basins, for example, subsidence is generally understood to occur in two phases. First, during a syn-rift phase, the lithospheric layers are stretched and thinned. Second, during a post-rift phase, the lithospheric or upper mantle cools back to a roughly pre-rift thickness. Conventional modeling approaches attempt to calculate lithospheric layer thicknesses through the use of different stretching factors for the crust and upper mantle lithospheric layers in a single fitting routine against the basin's tectonic subsidence curve; however, it has been found that such approaches have failed to accurately describe the evolution of a number of actual rift basins, in part due to a failure to consider the different processes in the lithospheric layers.